Author Archives: Eric

I hooked up two analog signal generators to the XY inputs of the HP 1338A Tri-Color XY display to display a Lissajou curve as a test of the inputs, and posted a video.

I’ve checked the basic functionality of the HP 1338A Tri-Color XY display using only its front panel controls, and posted a video.

I have an HP 9830A desktop computer, circa 1972, which runs BASIC using a custom bit-serial processor built out of TTL, with an architecture similar to the HP 2116 minicomputer. I’m planning to use the 9830A in my RetroChallenge entry, … Continue reading →

For RC2015/07, I’m going to hook up an old vector display (the retro part) to a modern microcontroller and either write a new game for it or port an old one. Vector displays were used on computers from the 1950s … Continue reading →

I’ve nearly finished tracing the Pacer control panel interface card schematic.  I haven’t yet traced the connections of one NOR gate of the 7425 at position 6A, and one inverter of the 7404 at position 5C. It’s possible that they’re … Continue reading →

I finished tracing the Pacer user memory card schematic. Most of it seems fairly obvious, except bus pin 25 and the E1/E2/E3 jumper. There are also some functional problems with this particular card.

The PACER memory board has sockets for four MM5204 512×8 EPROMs. The MM5204 is somewhat hard to come by, so I’ve designed a small adapter board to plug into an MM5204 socket and accept a common 2716 EPROM.  Only the … Continue reading →

At present the RAM on the user memory board in the PACER isn’t working correctly; the four most significant bits (D15..D12) are always reading as ones. Since this is true for all four banks of RAM (0000-00FF, 0100-01FF, 0200-02FF, and … Continue reading →

I’ve created a Github repository for my PACE assembler and simulator, which together with some very incomplete support for National’s IMP-16 multi-chip processor, I call ns16.  It is released under the GPLv3.  This was all work done back in 2009 … Continue reading →